High speed electronic remote medical imaging system and method

ABSTRACT

A medical imaging system with a base unit including an electronic display, and a remote imaging transducer connected to the display unit via a flexible cable. The cable includes a number of signal transmission lines, each of which includes a twisted pair of conductors for digital differential signal lines. Each conductor is connected at a first end to the transducer, and at a second end to the base unit. The signal transmission lines may be wrapped about a core, which may be an optical conduit communicating with a light source at the base unit.

REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of U.S. patent application Ser. No.09/916,728, filed Jul. 26, 2001, entitled CABLE HAVING SIGNAL CONDUCTORSSURROUNDING OPTICALLY TRANSMISSIVE CORE FOR REMOTE IMAGING SYSTEM, whichis incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to medical imaging systems having high speedmultiple-wire cables.

BACKGROUND OF THE INVENTION

Remote imaging systems are used to view objects not normally accessibleto human observation or conventional optical imaging tools. Onlylimited-size image transducers are positioned for viewing, and a signalis transmitted to a remote location for viewing. For instance, surgeonsuse optical imaging probes to view internal anatomy for diagnosis orsurgery. Such systems require miniaturized multi-wire cable assembliesto transmit image signals recorded by a charge coupled device (CCD) toan external display screen. Other medical imaging systems use anultrasound transducer that contacts the patient externally, to transmitan internal image via a multi-wire cable to an instrument for display.

For surgical and other applications, it is desirable to minimize thecable size. Limited diameter facilitates desired flexibility. However, adetailed real-time image needs significant bandwidth, requiring manyseparate conductors of a given frequency capability. To avoidundesirably bulky cables when substantial numbers of conductors arerequired, very fine conductors are used. To limit electrical noise andinterference at high signal frequencies, conductors are generallyshielded. A typical approach employs fine coaxial wires, which arebundled in a cable. Each wire includes its own shield, which providessuitable protection against interference at high frequencies.

While adequate, multiple coaxial assemblies have several disadvantages.The manufacturing cost of fine coaxial wiring is higher than isacceptable for many applications. The mode of terminating very finecoaxial wire is complex and expensive. And coaxial wires generateunwanted bulk due to the need for a given spacing between core conductorand shield.

SUMMARY OF THE DISCLOSURE

The present invention overcomes the limitations of the prior art byproviding a medical imaging system with a base unit including anelectronic display, and a remote imaging transducer connected to thedisplay unit via a flexible cable. The cable includes a number of signaltransmission lines, each of which includes a twisted pair of conductorsused for digital differential signaling. These twisted pairs maintainsignal integrity without a shield by utilizing the well known advantagesof differential signals, namely the elimination of signal radiation andthe reduction of common mode interference. Digital systems utilizingdifferential signaling include LVDS, SCI, Fiber Channel, and Firewire.Each conductor is connected at a first end to the transducer, and at asecond end to the base unit. The signal transmission lines may bewrapped about a core, which may be an optical conduit communicating witha light source at the base unit. The system may employ optical orultrasound imaging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away perspective view of a cable assembly according to apreferred embodiment of the invention.

FIG. 2 is a cut-away perspective view of a cable assembly componentaccording to the preferred embodiment of the invention.

FIG. 3 is a sectional end view of a cable assembly according to thepreferred embodiment of the invention.

FIG. 4 is a cut-away perspective view of an imaging system employing thecable assembly according to the preferred embodiment of the invention.

FIG. 5 is a view of an imaging system according to the preferredembodiment of the invention.

FIG. 6 is a view of an imaging system according to an alternativeembodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows a flexible cable assembly 10 for high frequency signal orhigh speed data transmission. The cable includes a core 12, a set oftwisted pair wires 14 helically wrapped about the core, and an outersheath portion 16.

The core has a flexible optical conduit provided by a bundle oflight-transmissive optical fibers 20. The fibers are wrapped by a spiralmetal armor layer 22 with an inside diameter of 0.160, and an outsidediameter of 0.200. The armor layer serves to provide a cylindrical shapethat does not deviate in cross section significantly under laterpressure, to preserve uniform spacing of the pairs from the axis of thecable. The armor is insulated by a helically-wrapped single band of thintape 23. The tape is a low-friction fluoropolymer film having athickness of 0.002 inch, a width of 0.125 inch, and wrapped with 45%overlap. In the preferred embodiment, the conduit is provided by 2050fibers, each of 0.66 Numerical Aperture and having a 70 micron diameter,with a fiber packing density of 80%, for an overall diameter of 3.5 mm.

The twisted pair wires 14 each include two helically twisted wiresinsulated from each other and encased in a conformal pair sheath as willbe discussed below. Nine twisted pairs are provided, although thisnumber may vary without limitation depending on the needs of theparticular application. Each twisted pair sheath has a diameter of 0.030inch, which allows each to abut the surface of the core throughout itsentire length, and to abut each adjacent pair sheath. This ensures thateach pair is kept at the same controlled distance from the coreconductor, and from the adjacent pairs.

In the preferred embodiment, the pairs wrap helically about the core.The wrap angle results in each pair making one full wrap about the coreover a cable length of 2.0 inches. The wrap angle may vary slightly toaccommodate variations in pair sheath diameter and core sheath diameter.If the pairs were sized to abut each other and the core, a slightvariance of the pair diameter above nominal, or of the core diameterbelow nominal would cause at least one pair to be forced away fromabutment with the core. However, an intended slight under-sizing of thepairs (and/or over-sizing of the core) prevents this problem. In thiscase, the expected gapping between pairs that would occur if they wereparallel to the core is prevented by helically wrapping them. The degreeof the wrap angle is in effect determined by the geometry of the pairsand core, with the wrap angle increasing (and the length for one fullhelical revolution of a pair decreasing) for smaller pair diameters.

The twisted pairs are helically wrapped by a single band of thin tape 26that holds the pairs against the core during intermediate manufacturingstages, and throughout the life of the cable. The tape is slightlytensioned to bias the pairs against the core, and to prevent gappingwhen the cable is flexed during usage. The tape is a low-frictionfluoropolymer film having a thickness of 0.004 inch. With a tape widthof 0.5 inch, and an outside diameter of the pair and core bundle of0.290 inch, the tape wraps with approximately 3 turns to the inch, witha 30% overlap between wraps.

A conductive shield 32 wraps closely about the bundle. The shield is abraided wrap of 38 AWG copper wire, with a specified coverage of atleast 90%. With the controlled dimensions of the spacer sheath, theshield is spaced equally from each wire pair.

An outer sheath 34 closely surrounds the shield with a wall thickness of0.030 inch, and provides protection against damage. The outer sheath isformed of flexible polyurethane, and is preferably co-extruded about theshield. The finished cable has an exterior diameter of 0.390 inches.

FIG. 2 shows a single twisted pair 14 in detail. Each wire of the pairhas a conductor 40 of 32 AWG copper, surrounded by an insulating sheath42 of 0.003 inch wall thickness fluropolymer material. Each sheathedwire has an outside diameter of 0.015 inch. The wires are wound in ahelix with a twist rate of 3 full turns per inch. In some applications,the twist rates may be engineered at different rates to avoid unwantedinterference between adjacent pairs. For example, the twist rates mayalternate between two different values so that adjacent pairs do notinteract. The wires are in contact with each other along their entirelength, on an axis. In the preferred embodiment, the wires are encasedin a cover 44 of polymeric material. The cover is co-extruded about thewires, with an outside diameter of 0.045 inch, or 1½ times the diameterof the pairs.

As illustrated and described in the preferred embodiment, it has beenfound that the cable enables data rates of 100 to 655 Mbits/sec perpair. This is for cables with a length of 18 to 120 inches. While thevery fine wires employed are needed to ensure flexibility forapplications where a connected component must be moved comfortably (suchas for input devices or transducers connected to computing equipment orelectronic instruments), it is believed that longer cable lengthsrequired for other purposes will require larger conductors. Althoughthese may employ the concepts disclosed and illustrated for thepreferred embodiment, they are less suited where repeated flexibility isneeded.

As shown in FIG. 3, some of the wires wrapped about the core may not betwisted pairs. In the illustrated embodiment, there are six wires havinga solid core for power and other higher current needs, while the twistedpairs serve to transmit the low voltage differential signals. Inalternative embodiments, all wires may be twisted pairs, or differentnumbers or proportions of twisted pairs may be used.

The cable 10 is employed in an imaging system 50 as shown in FIG. 4. Thesystem includes an instrument 52, the cable 10, and a camera 54. Thecable 10 has a first end 56 connected to the instrument, and a secondend 60 connected to the camera.

The instrument has a housing 62 with a connector 64. A fiber opticconduit 66 extends within the housing from the connector 64 to anillumination source such as a light bulb 70, via a concentrating lens 72that couples the light source to the conduit. A set of electrical wires74 extends from the connector to an electronic circuit element 76 in thehousing. An electronic display screen 80 is electronically connected tothe circuitry. The circuitry serves to receive an electronically encodedmoving image information via the cable, and decodes it for display onthe screen.

The instrument connector includes an interface suitable for coupling theoptical conduit 66 in the housing with the optical fiber bundle 20 ofthe cable. Similarly, the connector includes components to connect thewiring 74 with the wires of the cable. In an alternative embodiment, thecable may be permanently attached to the housing, so that no connectoris required, and so that the optical fibers extend fully to the lightsource, and the cable wires connect directly to the circuitry.

The camera 54 is a compact device having a housing 82 defining a chamber84 in which a charge-coupled device (CCD) 86 is contained. Inalternative embodiments, any electronic image transducer suitable forgenerating an electronic signal that may be decoded for re-generation ofan image formed on the transducer surface may be employed. A lens 90 inthe housing is positioned on axis with the imaging surface of the CCD,to form an image of an object 92 on the imaging surface. The wires 14 ofthe cable are connected to the CCD, so that a corresponding electronicimage 92′ is displayed on the screen 80.

Illumination of the object is provided by the light transmitted by thefiber optic bundle. The end of the fiber bundle 20 is located adjacentto the imaging lens 90, so that emitted light shines in the direction ofthe optical axis of the lens. In an alternative embodiment, the fiberends may be distributed coaxially about the imaging lens. In operation,the camera is positioned away from the instrument, and adjacent to theobject imaged. In medical applications, the camera may be internallypositioned in a patient. The camera may be mounted together withsurgical instruments such as endoscopes.

For instance, FIG. 5 shows the imaging system 50 in which a surgeon 100has inserted the camera 54 into an incision 102 in a surgical patient.The light source in the base unit 52 is carried through the opticalfibers in the cable 10 to the camera. The light illuminates the fieldinternal to the patient, so that light reflected off the tissues in thepatient generates the image on the CCD. This image is converted to anelectronic signal that is returned to the base unit via the high speedtwisted pairs using Low Voltage Differential Signal (LVDS) transmission,whereupon the signal is converted to an image that is displayed forobservation by the surgeon in real time during the surgery. Althoughillustrated with the display unit integral with the instrument forsimplicity, in many applications, a separate display may be positionedwithin the surgeon's field of view in another location, or theinstrument positioned for direct viewing during surgery.

FIG. 6 shows an alternative ultrasound medical system 120. An ultrasoundbase unit 122 has an ultrasound transducer unit 124 connected by aflexible cable 126. The cable 126 is comparable to the cable 10 of FIGS.1-5, except that it does not employ the optical fiber conduit, sinceultrasound imaging does not require illumination. A central coreconductor of greater size than the twisted pair conductors may besubstituted, and used to provide power to the transducer. The twistedpairs may surround the core in the same manner as in cable 10.

The physician or technician 130 applies the transducer unit externallyin contact with the patient 132. Ultrasonic energy is emitted by thetransducer into the patient's tissues, which reflect the energy back ina pattern that reveals the nature and position of the tissues. Thisenergy pattern is converted to a high-bandwidth electronic signal thatis returned to the base unit via the high speed twisted pairs using LowVoltage Differential Signal (LVDS) transmission. The signal is thenreconverted for display as a real time moving image on a display screen134 on the base unit, for viewing.

While the above is discussed in terms of preferred and alternativeembodiments, the invention is not intended to be so limited. Forinstance, the medical use of twisted pairs for LVDS transmission ofsignals from flexibly connected transducers need not be limited toendoscopy and ultrasound imaging. Any medical application where imagesmust be made of subjects remote from a display unit may employ suchfeatures. This may include external imaging cameras used for dentistry,conventional surgery, robotic surgery, minimally invasive surgery(arthroscopic, laproscopic), internal diagnostics, opthalmic and otherfields in which close, high-resolution visual inspection and medicalanalysis is required and where flexibility of cabling is needed.

What is claimed is:
 1. A medical imaging system comprising: a base unitincluding an electronic display; a remote imaging transducer connectedto the display unit via a flexible cable; the cable including aplurality of signal transmission lines; and each signal transmissionline including a pair of conductors coupled for low voltage differentialsignal transmission.
 2. The system of claim 1 wherein the cable includesan optically transmissive element connected at one end to anilluminator, and operable to transmit light to a subject imaged by thetransducer.
 3. The system of claim 2 wherein each of the signaltransmission lines is wrapped about the optically transmissive element.4. The system of claim 1 wherein the transducer is a photosensitiveelectronic device.
 5. The system of claim 1 wherein the transducer is anultrasound element.
 6. The system of claim 1 wherein the conductors ofeach signal transmission line are of a common wire gauge, and are eachhelically would about each other.
 7. The system of claim 1 wherein thesignal transmission lines are evenly spaced apart from an axis definedby the core.
 8. A method of medical imaging comprising the steps:positioning a transducer adjacent a patient; generating an electricalsignal in the transducer to represent an image; transmitting the signalvia a flexible cable connected to a base unit, including transmittingseparate signals via a plurality of pairs of conductors, employing lowvoltage differential signal transmission; and in the base unit,displaying an image based on the signal.
 9. The method of claim 8wherein transmitting signals includes transmitting signals via twistedpairs of wires.
 10. The method of claim 8 including illuminating asubject portion of the patient imaged by the transducer via an opticalconduit in the cable.
 11. The method of claim 8 wherein generating anelectrical signal in the transducer includes forming an image on aphotosensitive electronic device.
 12. The method of claim 8 whereingenerating an electrical signal in the transducer includes receivingemitted ultrasound energy.